Biosensors such as glucose sensor (strip type and continuous monitoring type), electrocardiogram, blood pressure, and the like use batteries in its controllers or monitors. The batteries can be in the form of rechargeable or disposable batteries. The batteries are usually monitored to ensure that there is sufficient power to complete many of the tasks assigned to the sensors. For diagnostic purposes, the batteries' state or charge or other operating parameters can be periodically recorded with the biosensor measurement results and stored in static or non-volatile memory so that performance of the device or the battery can be tracked over the lifetime of the device. However, the non-volatile memory may have only a limited amount of storage allocated to both measurement results and device diagnostic data. In the event that the device runs out of memory, the oldest memory is deleted, which deleted memory may include the battery records.